What this 8 A sensitive-gate TRIAC does on the board
The BTB08-600TWRG is an 8 A RMS, 600 V off-state TRIAC from STMicroelectronics, housed in a TO-220 through-hole package. It switches AC loads — heaters, small motors, lighting — where the gate is driven directly from a logic-level source like a microcontroller or a low-power sensor output.
Gate trigger and hold current — the bench-fit numbers
The holding current (Ih) is 10 mA max, meaning the TRIAC stays latched once triggered as long as the load current stays above that threshold; below it the device turns off at the next zero-crossing.
Surge current and thermal robustness
Non-repetitive surge current (Itsm) is rated 80 A at 50 Hz and 84 A at 60 Hz — this covers the inrush from a cold incandescent lamp filament or a capacitor-input power supply.